The MTO process has been described in US 2006 0235251, WO 2005 016856, US 2006 0063956, US 2006 0161035, U.S. Pat. No. 6,207,872, US 2005 0096214, U.S. Pat. No. 6,953,767 and U.S. Pat. No. 7,067,095.
Ethylene and propylene are particularly desirable olefins but it has been found that their yields in the MTO process are reduced by the production of medium weight hydrocarbons such as C4, C5 and C6 olefins, as well as some heavier components. Methods are needed to alter the product distribution in the MTO process for making light olefins to provide processing flexibility. Methods are sought to reduce the production of O4, C5 and higher olefins from the MTO process relative to the production of ethylene and propylene. Therefore an OCP process is combined with the MTO process to crack the C4, C5 and higher olefins from the MTO process. Such yield improvements of ethylene and propylene significantly improve the economies of the methanol to olefins process.
WO1999 018055 relates to a method for increasing light olefin yield during conversion of oxygenates to olefins comprising: contacting an oxygenate feed in a first reactor (MTO reactor) with a non-zeolitic molecular sieve catalyst under first conditions effective to produce a first product comprising light olefins and a heavy hydrocarbon fraction; separating said light olefins from said heavy hydrocarbon fraction; feeding said heavy hydrocarbon fraction to a second reactor; and subjecting said heavy hydrocarbon fraction in said second reactor to second conditions effective to convert at least a portion of said heavy hydrocarbons to light olefins. Suitable SAPO's for use in the MTO reactor include SAPO-11, SAPO-44, SAPO-34, SAPO-17, and SAPO-18. A preferred zeolite for the auxiliary reactor is ZSM-5.
US 2004 0102667 relates to a process for the production of light olefins from an oxygenate-containing feed stream. This invention more particularly refers to a process for increasing yields of light olefins through cracking of heavier olefins produced in a methanol to olefins process.
It has been discovered that, in a combined MTO OCP process, the use of a specific catalyst in the MTO reactor leads to very high yields in propylene. Said specific catalyst is made of metalloaluminophosphate (MeAPO) molecular sieve with lamellar crystal morphology having an empirical chemical composition on an anhydrous basis, after synthesis and calcination, expressed by the formula HxMeyAlzPkO2 wherein,y+z+k=1x<=y y has a value ranging from 0.0008 to 0.4 and advantageously from 0.005 to 0.18z has a value ranging from 0.25 to 0.67 and advantageously from 0.38 to 0.55k has a value ranging from 0.2 to 0.67 and advantageously from 0.36 to 0.54said molecular sieve having predominantly a plate crystal morphology in which the width (W) and the thickness (T) are such as:W/T is >=10 and advantageously ranges from 10 to 100.
In a preferred embodiment T is <=0.15 μm, more desirably <=0.10 μm, more desirably <=0.08 μm, advantageously ranges from 0.01 to 0.07 μm and preferably from 0.04 to 0.07 μm.
Said MeAPO are prepared in the presence of one template, one texture influencing agent, inorganic metal source, Al and P source, all these ingredients being in specific proportions, MeAPO with very thin lamellar plate crystal morphology are obtained. The template can be tetraethylammonium hydroxide (TEAOH) or an amine. The texture influencing agent can be an alcohol, a diol or glycerol.
The following prior arts describe MeAPO but they are not in the shape of thin lamellas. All these prior arts concern MeAPO with lamellar cubic or plate crystal morphology. In all these prior arts only one template is used. Moreover the combination MTO-OCP is not described.
U.S. Pat. No. 4,440,871 describes microporous crystalline silicoaluminophosphates (referred as SAPO) the pores of which are uniform and have nominal diameters of greater than about 3 Angstroms and whose essential empirical chemical composition in the as-synthesized and anhydrous form is mR:(SixAlyPz)O2 wherein “R” represents at least one organic templating agent present in the intracrystalline pore system; “m” has a value of from 0.02 to 0.3; “m” represents the moles of “R” present per mole of (SixAlyPz)O2; “x”, “y” and “z” represent the mole fractions of silicon, aluminum and phosphorus respectively, present as tetrahedral oxides, said mole fractions being such that they are within a specific area in the ternary diagram SixAlyPz. Process for preparing said SAPO comprises forming a reaction mixture containing reactive sources of SiO2, Al2O3, and P2O5 and an organic templating agent, said reaction mixture having a composition expressed in terms of molar oxide ratios of: aR2O:(SixAlyPz)O2:bH2O wherein “R” is an organic templating agent; “a” has a value large enough to constitute an effective amount of “R” and is within the range of greater than 0 to 3; “b” has a value of from zero to 500; “x”, “y” and “z” represent the mole fractions, respectively, of silicon, aluminum and phosphorus in the (SixAlyPz)O2 constituent and each has a value of at least 0.01 and crystallizing the reaction mixture thus formed at a temperature of at least 100° C. until crystals of the silicoaluminophosphate are formed.
U.S. Pat. No. 6,207,872 relates to a process for converting methanol to light olefins comprising contacting the methanol with a catalyst at conversion conditions, the catalyst comprising a crystalline metallo aluminophosphate molecular sieve having a chemical composition on an anhydrous basis expressed by an empirical formula of: (ELxAlyPz)O2 where EL is a metal selected from the group consisting of silicon, magnesium, zinc, iron, cobalt, nickel, manganese, chromium and mixtures thereof, “x” is the mole fraction of EL and has a value of at least 0.005, “y” is the mole fraction of Al and has a value of at least 0.01, “z” is the mole fraction of P and has a value of at least 0.01 and x+y+z=1, the molecular sieve characterized in that it has predominantly a plate crystal morphology, wherein the average smallest crystal dimension is at least 0.1 micron and has an aspect ratio of less than or equal to 5.
U.S. Pat. No. 6,334,994 relates to a microporous crystalline silico-alumino-phosphate composition, the theoretical composition of which, on a water-free basis after synthesis and calcination, is: HwSixAlyPzO2 where w and x have a value between 0.01 and 0.05 and y and z are values between 0.4 and 0.6, wherein the composition is a mixed phase product comprising silico-alumino-phosphates of AEI and CHA structure prepared in one batch crystallization, not including mere physical mixtures, the product after calcination in air at 550° C. for 4 hours, produces a specific X-ray diffractogram and XRD-profiles.
EP 893159 relates to a method for preparing catalysts comprising silica-modified crystalline silicoaluminophosphate molecular sieves, which comprises adding an aluminum alkoxide to an aqueous amine or organic ammonium salt solution cooled at a temperature of not higher than 20° C., followed by hydrolysis, until a uniform aqueous aluminum hydroxide colloid or solution is formed, adding, to the colloid or solution, silica or other Si-source compounds, and phosphoric acid or other P-source compounds, if desired, along with a metal source selected from the group of Li, Ti, Zr, V, Cr, Mn, Fe, Co, Zn, Be, Mg, Ca, B, Ga and Ge, hydrothermally treating the resulting mixture to prepare a crystalline silicoaluminophosphate molecular sieve, and then modifying the crystalline silicoaluminophosphate molecular sieve with silica.
US 2005 0096214 (U.S. Pat. No. 6,953,767) relates to a process for making an olefin product from an oxygenate feedstock comprising contacting said oxygenate feedstock with a catalyst comprising a silicoaluminophosphate molecular sieve comprising at least one intergrown phase of molecular sieves having AEI and CHA framework types, wherein said intergrown phase has an AEI/CHA ratio of from about 5/95 to 40/60 as determined by DIFFaX analysis, using the powder X-ray diffraction pattern of a calcined sample of said silicoaluminophosphate molecular sieve, under conditions effective to form an olefin product.
It also describes a method for preparing the molecular sieve of said process that comprises
(a) combining a reactive source of silicon, a reactive source of phosphorus and a hydrated aluminum oxide in the presence of an organic structure directing agent (template) to form a mixture;
(b) mixing and heating continuously the mixture prepared at step a) up to the crystallization temperature;
(c) maintaining the mixture at the crystallization temperature and under stirring for a period of time of from 2 to 150 hours;
(d) recovering crystals of the silicoaluminophosphate molecular sieve
(e) wherein the mixture prepared at step a) has a molar composition within the following ranges:
P2O5:Al2O3 from 0.6:1 to 1.2:1
SiO2:Al2O3 from 0.005:1 to 0.35:1
H2O:Al2O3 from 10:1 to 40:1
and the template is a tetraethylammonium compound.
In all these above prior arts only template and/or specific reaction conditions are used to influence the crystal structure of the material. In the following U.S. Pat. No. 6,540,970 a template and a solvent of the metal (Me) source are used. In the examples the organic silicon source is tetraethylorthosilicate. U.S. Pat. No. 6,540,970 relates to a method for making a metalloaluminophosphate (MeAPO) molecular sieve, said process comprising the steps of:
providing a source of alumina, a source of phosphorus, water, and a template suitable for forming a MeAPO molecular sieve;
providing a source of metal including metal particles, said metal particles measuring, in their largest dimension, equal to or less than five nanometers;
providing a water soluble organic solvent capable of solubilizing said source of metal;
forming a synthesis mixture from said source of alumina, said source of phosphorus, said water, said template, said source of metal, and said solvent;
and forming a MeAPO molecular sieve from said synthesis mixture. Desirably, the water soluble organic solvent capable of solubilizing the source of the metal is selected from the group consisting of sulfoxides and C1 to C5 oxygenated hydrocarbons. Desirably, the oxygenated hydrocarbon is selected from the group consisting of alcohols (branched or normal), ketones, aldehydes, diols and acids. Useful solvents include one or more solvents selected from the group consisting of acetone, 1,2-propanediol, 1,3-propanediol, methanol, ethanol, propanol, isopropanol, butanol, and ethylene glycol. Desirably, the solvent is an alcohol. The products obtained are isocrystalline spheroidal particles comprising a SAPO molecular sieve. The particle measures from 0.5 microns to 30 microns in diameter.